The potential for the presence of pathogenic bacteria, viruses, and fungi in biological fluids such as saliva, tears, blood, and lymph is of significant concern to health care workers and patients. Surfaces contaminated with bacteria, viruses, and fungi can facilitate the spread of infections. Additionally, the usefulness of valuable food and industrial products can be destroyed by the presence of bacteria and viruses. Methods for minimizing the transmission of pathogens (for example, in the home, in hospitals, and in day-care centers) are therefore important.
Microorganisms can be killed or rendered static by a number of physical and chemical methods. Physical methods include the application of heat and/or radiation. Chemicals that have been used to limit viral, fungal, and bacterial growth include alcohols (usually, 70 percent by volume aqueous ethyl or isopropyl alcohol); phenol and phenol derivatives such as hexachlorophene; formaldehyde; glutaraldehyde; ethylene oxide; ether; detergents; chlorhexidine gluconate; heavy metals such as silver, gold, copper, and mercury; organic compounds of mercury such as mercurochrome; and oxidizing agents such as hydrogen peroxide, iodine, hypochlorite, and chlorine.
Antibiotics, such as bacitracin, the cephalosporins, cycloserine, the penicillins, vancomycin, chloramphenicol, the erythromycins, the tetracyclines, the sulfonamides, and the aminoglycosides (such as streptomycin, neomycin, and gentamycin) have traditionally been defined as chemicals made by microorganisms that can kill bacteria. Antibiotics have no effect on viruses.
Semiconductor photocatalysts (for example, oxides of titanium, zirconium, zinc, tin, iron, tungsten, and molybdenum) have been used for the destruction (by photochemical oxidation) of organic contaminants in fluid media. Titanium dioxide has been widely investigated because of its chemical stability, suitable bandgap structure for ultraviolet/visible photoactivation, and its relatively low cost. Co-catalysts (for example, platinum, palladium, silver, and/or oxides and sulfides of these metals) have been added to titanium dioxide to increase its photocatalytic activity.
More recently, nanosize titanium dioxide particles have been utilized and have been capped with a variety of noble metals to improve their photocatalytic efficiency. Gold-capped titanium dioxide nanocomposites have been formed from a mixture of titanium dioxide solution and a gold salt (for example, HAuCl4) by the reduction of gold on the surface of the titanium dioxide nanoparticles using chemical or photochemical reduction methods. Such nanocomposites have been dispersed in aqueous media and shown to inhibit microbial growth in the presence of light.
Each of the foregoing antimicrobial agents (as well as other known antimicrobials) has its own set of advantages and disadvantages. Some are toxic, costly, or otherwise impractical as routine disinfecting compounds. Some are unstable and become inactive over time. Some function such that the target microorganism develops resistance to the antimicrobial agent.